WEDNESDAY, June 5 (HealthDay News) -- Billions of people around the world have untreated tooth decay, a new study has found.

Researchers from the Institute of Dentistry at Queen Mary, University of London, discovered that dental problems affect up to 3.9 billion people -- more than half of the world's population.

"There are close to 4 billion people in the world who suffer from untreated oral health conditions that cause toothache and prevent them from eating and possibly sleeping properly, which is a disability," study leader Wagner Marcenes said in a university news release. "This total does not even include small cavities or mild gum diseases, so we are facing serious problems in the population's oral health."

As part of a systematic assessment of global data on 291 major diseases and injuries in 2010, the researchers found untreated tooth decay or cavities in permanent teeth were the most common, affecting 35 percent of the global population.

The study, published recently in the Journal of Dental Research, also showed that oral conditions accounted for 15 million disability-adjusted life-years globally, suggesting an average health loss of 224 years per 100,000 people.

Moreover, the global burden of oral conditions increased 20 percent between 1990 and 2010, primarily due to population growth and aging. The global burden of oral problems is also shifting from severe tooth loss to severe gum disease and untreated cavities, the researchers said.

"Tooth loss is often the final result when preventive or conservative treatments for tooth decay or gum disease fail or are unavailable," Marcenes said. "It is likely that current dental services are coping better to prevent tooth loss than in the past, but major efforts are needed to prevent the occurrence and development of gum diseases and tooth decay."

"Ironically, the longer a person keeps their teeth, the greater the pressure on services to treat them," he said.

The most significant increases in the burden of oral conditions were seen in Oceania and east central and sub-Saharan Africa.